Design And Implementation Of Dual-Code Fast Synchronous Spread Spectrum System

Spread spectrum communication technology is widely used in military and civil communication because of its good anti-jamming,confidentiality and anti-multipath capability.Direct sequence spread spectrum communication system is one of the most widely used in spread spectrum communication systems,and synchronization technology is the core technology in direct sequence spread spectrum communication system,its performance will directly affect the performance of the spread spectrum communication system.Therefore,the research of synchronization technology,especially the research of rapid synchronization technology is of great significance.In the traditional spread spectrum communication system,the spread spectrum code is used to realize the spread spectrum modulation of the data,and then multiplied by the carrier to realize the carrier modulation.The demodulation is carried out by using the coherent carrier generated by the carrier tracking loop of receiver,and despreading is realized by using the capture and tracing technique of the spread spectrum code to obtain the data information of transmitter.In this thesis,the traditional spread spectrum communication system is optimized and improved,and a dual-code fast synchronous spread spectrum system is proposed.At the receiver,the carrier tracking loop is not necessary to generate coherent carrier wave,so that the time spent in synchronization is reduced.By adding a spreading code at the transmitter,the dual-code is used to realize the spread-spectrum modulation of the data,and the carrier tracking loop of the receiver are removed,and the digital matched filter method is used to capture the signal processed by digital down conversion technology.The system reduces the entire system capture time,obtains the original data of the transmitter fast and efficiently.Then,For a high dynamic environment will produce Doppler frequency offset and frequency offset between the local oscillator of the transmitter and receiver,a frequency offset estimation method based on the principle of monopulse angle measurement is proposed.By comparing the relationship between the output peak signal and the frequency offset lead and lag,the magnitude and direction of the frequency offset are estimated,and then the frequency offset is compensated to eliminate the influence of frequency offset to output correlation peak of digital matched filter and to improve the system capture performance.Next,the simulation scheme is verified on the MATLAB platform.The simulation results show the feasibility of the system scheme,and the performance of the system is analyzed from the aspects of detection probability,false alarm probability and bit error rate.Finally,the proposed system is designed and implemented on the hardware platform,using Quartus II development environment programming to achieve the design of the transmitter and the receiver,with the help of ModelSim tools and SignalTap II tools for signal analysis and functional simulation,to verify the hardware implementation of the proposed scheme.The scheme of this paper has certain directive function to the practical engineering application,and also provides a new way for the research and development of fast synchronization technology.